As Giant was just a giant human instead of a costume kaiju, I have little to tell you about the making of the character (There is nothing to talk about regarding the making of Giant Morpho either as you may expect).
While the man who became giant was named Koji in the show, it came from Koji Ishizaka who served as the narrator for “Ultra Q” and the first half of the series “Ultraman” because Kyoko Kitazawa who wrote the script of this episode had known Ishizaka since they were university students through workshops sponsored by broadcast writers.
Koji Kajita who directed this episode, however, is said to have jokingly complained about the name as the heroin kept calling his name throughout the episode.
It seems that this episode story originated from the idea worked out by Tetsuo Kinjo based on a folktale in which the leading character transforms into a dragon.
It is said that they were also thinking about the likeliness of another ending for this episode in which Giant spoke to the heroin asking her why she left him behind when he had become giant.
In that version of the script, Koji was to die after he returned to normal size by being exposed to Heat Atomic X-ray saying, “I just wanted your heart…”
It is good to know that their love made a miracle happen in the end in the aired version of the episode with the theme to question if love would remain unchangd even if the significant other has turned into a giant.
Kozo Nomura (1931-present) who acted Koji seems to have retired from show business although he is also known among Ultra fans for his role as Dr. Miyabe in Ultraseven Episode 19.
Machiko Naka (1936-present) who played the heroin Ayako is doing well and appeared in an interview covered in a book. She is also known as Mrs. Ishiguro she played in Ultraseven Episode 2, and it is likely that she is very happy about her appearances in each episode.